Multiregional whole‐genome sequencing of hepatocellular carcinoma with nodule‐in‐nodule appearance reveals stepwise cancer evolution

Abstract

Recent genetic analyses revealed genetic heterogeneity in hepatocellular carcinoma (HCC), although it remains unclear how genetic alterations contribute to the multistage progression of HCC, especially the early step from hypovascular liver nodules to hypervascular HCC. We conducted multiregional whole-genome sequencing on HCCs with a nodule-in-nodule appearance, consisting of inner hypervascular HCC surrounded by hypovascular HCC arising from a common origin, and identified point mutations, structural variations, and copy-number variations in each specimen. According to the genetic landscape of the inner and outer regions, together with the pathological and radiological findings, we examined the stepwise evolution of cancer cells from slow-growing HCC to rapid-growing HCC. We first demonstrated that most tumor cells consisting of hypovascular well-differentiated HCCs already harbored thousands of point mutations and even several structural variations, including chromosomal translocations and chromothripsis, as the trunk events. Telomerase reverse transcriptase (TERT)-associated aberrations, including promoter mutations, chromosomal translocation, and hepatitis B virus DNA integration, as well as abnormal methylation status, were commonly detected as the trunk aberrations, while various liver cancer-related genes, which differed in each case, had additionally accumulated in the inner dedifferentiated nodules. Further, differences in the trunk and branch mutational signatures suggested a multistep contribution to the mutagenesis in each case. In conclusion, genomic alterations associated with the TERT gene could be the key driver events to form the hypovascular HCC, and additional case-specific driver mutations accumulate during the progression phase, forming intra-and inter-tumoral heterogeneity, confirming the importance of genetic testing before targeting therapy. These data shed light on the process of multistep hepatocarcinogenesis and will be helpful toward investigating new therapeutic strategies for HCC.

Hepatitis B virus–induced hepatocarcinogenesis: A virological and oncological perspective

“…14 HCC originates from hepatocytes in cirrhotic liver tissue in most cases and develops through a multistep process. 15 HBV-related and immunemediated persistent inflammation leads to immune imbalance in the intrahepatic mileu. 16 While hepatic stellate cells respond to the chronic damage with fibrogenesis, the premalignant senescent hepatocytes affect adaptive intrahepatic immunity that blocks the hepatocarcinogenesis in unaffected patients.…”

“…These can be related to a complex pattern involving tumour suppressor gene (TSG) dysfunction (p53 inactivation), tumour-promoting gene activation via micro-RNAs (miRNA), increased telomerase activity, TSG hypermethylation and mitochondrial dysfunction associated with JAK/STAT4 pathway activation. 15 HBV-DNA integration occurs in open chromatin regions and close to early replicated and highly expressed genes. Moreover, viral replication is related to the number of integrated copies as a multistep process from a single cell.…”

“…It is still debated whether HCC cells arise from senescent hepatocytes or liver stem cells 14 . HCC originates from hepatocytes in cirrhotic liver tissue in most cases and develops through a multistep process 15 . HBV‐related and immune‐mediated persistent inflammation leads to immune imbalance in the intrahepatic mileu 16 .…”

“…First, HBV genome integration in the hepatocyte chromosome or HBV‐derived protein recruitment on hepatocyte chromatin may result in some oncogenesis‐related processes. These can be related to a complex pattern involving tumour suppressor gene (TSG) dysfunction (p53 inactivation), tumour‐promoting gene activation via micro‐RNAs (miRNA), increased telomerase activity, TSG hypermethylation and mitochondrial dysfunction associated with JAK/STAT4 pathway activation 15 . HBV‐DNA integration occurs in open chromatin regions and close to early replicated and highly expressed genes.…”

“…In some cases, HBV integration can lead and promote HCC initiation in cirrhotic or non‐cirrhotic livers, since it is associated with alterations of cancer‐driven genes located at a distance. Another relevant aspect of the carcinogenetic process regards the insertional mutagenesis, which leads to genomic instability 15,52 . The genomic instability may also arise due to viral proteins affecting mitotic checkpoint regions on hepatocyte chromosomes.…”